Perhaps you should try some spelling variations:
"improving voluntary performance review." » "improving country performance review.", "improving entry performance review.", "improving industry performance review.", "improving voluntary performance risk.", "improving voluntary performance evidence."
"improving urban performance series." » "improving urban performance studies.", "improving urban performance size.", "improving bank performance series.", "improving loan performance series.", "improving human performance series."

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("improving urban performance series.") or ("improving voluntary performance review."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving urban performance series.") OR ("improving voluntary performance review.")).
• Removing quotes may allow a broader search: (( improving urban performance series. ) or ( improving voluntary performance review. )).
• Adding a wildcard symbol may retrieve word variants: (("improving urban performance series.") or ("improving voluntary performance review."))*.